The present invention relates generally to regulator/converter circuits for use in power supplies and more specifically, to a buck regulator/converter circuit that is capable of providing at least two different output voltage levels.
A large number of machinery use DC voltage for operation. The DC voltage may be supplied either by a battery or by an AC power source that has been stepped down by a transformer and rectified by a diode bridge. Because voltage from a battery or rectifier bridge is fixed and unregulated, many systems also include a DC-to-DC regulator/converter intermediate between the power source and the rest of the machinery. The DC-to-DC regulator/converter regulates/converts the unregulated power from the battery or rectifier bridge into a regulated DC power source for use by the machinery. The DC-to-DC regulator/converter may also decrease or increase the voltage output by the DC-to-DC converter.
As an example, many welding and cutting systems use an AC voltage source for power. The AC voltage source is rectified and provided to a DC-to-DC regulator/converter. The DC-to-DC regulator/converter regulates the voltage and provides a controlled output DC voltage for use in the welding or cutting system to initiate and maintain the welding or cutting process.
A common DC-to-DC regulator/converter used in the industry is referred to as a xe2x80x9cbuckxe2x80x9d regulator. A buck regulator typically not only regulates the ripple in the DC output, but it also steps down the DC output voltage level from that of the voltage input into the buck regulator. With reference to FIG. 1, a conventional buck regulator 10 typically includes positive and negative input terminals, 12a and 12b, respectively, connected to either a battery or a rectifier bridge and AC power, not shown. The regulator further also includes positive and negative load terminals, 14a and 14b, respectively, connected across a load, not shown. Connected to the positive terminal 12a is a switch QB for regulating the voltage output by the regulator. The buck regulator also includes a freewheeling diode DB, an inductor LB, and a capacitor CB.
In operation, the switch QB is alternately switched between xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d states. In the xe2x80x9conxe2x80x9d state, power from the input source is provided to the load. In the xe2x80x9coffxe2x80x9d state, current flows from the charged inductor LB through the load and the freewheeling diode. This configuration regulates the load voltage and steps down the input voltage before it is applied to the load.
Although conventional Buck regulators/converters, such as the one illustrated in FIG. 1, typically provide acceptable regulated DC voltage outputs for most machinery, there are some drawbacks with many conventional buck regulator/converter designs. One problem is the use of only one switch for power regulation. As illustrated in FIG. 1, the entire load current in the regulator/converter is conducted through the switch QB when the switch is in the xe2x80x9conxe2x80x9d state. As such, in applications in which the load current is at a relatively high level, the switch may be deleteriously affected. Due to the increased current requirements, a higher rated, more costly switch must be used for high current level applications. This, in turn, may increase the overall cost of the machinery in which the buck regulator circuit is implemented.
Another noted problem is that conventional buck regulator circuits are typically designed to output only one particular voltage level, as opposed to a range of voltage levels. Some applications, however, could benefit from use of more than one voltage level. For example, in a welding or cutting system, typically a higher voltage level is needed to initiate a welding or cutting process, but only a lower voltage level is required to maintain the welding or cutting process, once initiated. However, because conventional buck regulators are only designed for one voltage output, conventional welding or cutting systems typically design the buck regulator to output the maximum voltage needed for initiating welding or cutting and use this same voltage for the entire process. As such, use of conventional buck regulators having only one voltage output may be energy inefficient.
As set forth below, the present invention provides a modified buck regulator circuit that overcomes many of the deficiencies associated with providing regulated DC power to machinery. In particular, the present invention provides a modified buck regulator/converter that reduces the peak current across the switch. The present invention also allows for the output of different voltage levels, to provide a more energy efficient system.
For example, in one embodiment, the present invention provides a buck regulator circuit comprising positive and negative input terminals for connection to a DC source, such as either a battery or a transformer and bridge rectifier. The circuit further includes positive and negative load terminals for connection to a load. Connected between the positive and negative terminals is an inductive element. Further, and importantly, the buck regulator circuit includes an auto-transformer having first and second end taps and an intermediate tap. The intermediate tap is connected to the negative load terminal. Connected to each of the first and second end taps of the auto-transformer are respective first and second switches. The switches are also connected to the negative input terminal of the circuit. Further, first and second diodes are also connected respectively between the first and second end taps and the positive load terminal.
In operation, the switches may be operated in either a parallel or push-pull mode. In a parallel mode in which the switches are switched to the xe2x80x9conxe2x80x9d state at the same time and xe2x80x9coffxe2x80x9d state at the same time, the buck regulator of the present invention provides a first voltage level across the positive and negative load terminals. Further, because the two switches are in parallel with one another, the current flowing through the load is divided between the two switches. As such, each switch is not required to handle all of the current across the load. Thus, lower cost switches having lower current ratings may be used in the buck regulator of the present invention, as opposed to conventional buck regulator circuits.
Alternatively, operating the switches in a push-pull mode also provides several advantages. Specifically, when operated in this configuration, the buck regulator circuit of the present invention provides a second output voltage across the load that is less than the first voltage provided in the parallel mode configuration. Further, the buck regulator circuit in the push-pull mode also decreases the current through each switch.
Specifically in the push-pull mode, the first and second switches are alternately switched between xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d states, such that when one switch is xe2x80x9conxe2x80x9d at a given time the other switch is xe2x80x9coff.xe2x80x9d When each switch is switched to an xe2x80x9conxe2x80x9d state, the auto-transformer steps down the current by approximately one half of the load current, such that the switch only receives half the current. Further, and importantly, the auto-transformer also steps down the voltage across the load to provide a voltage that is approximately one-half the voltage provided across the load during parallel mode operation of the switches.
As such, depending on whether the switches of the present invention are operated in a parallel or push-pull operation, the buck regulator circuit of the present invention may provide two separate voltages. Further, in either mode, the current across the switches is less than that of conventional circuits that use only one switch.